Several emerging theories of addiction have described how substance abuse impacts decision-making processes and creates impulsive behavior. But less is known about the way substance abuse affects specific components of decision-making. : Does drug use alter the way rewards are valued or the perception of the costs (e.g., risk) associated with obtaining them?

A new study from researchers at the University of Washington (UW) concludes that adolescent alcohol use corrupts decision-making later in life. It does so by changing the perception of risk but not how rewards are valued. The findings provide insight into the specific consequences of adolescent alcohol use on decision making, according to researchers. The study, "Risk preference following adolescent alcohol use is associated with corrupted encoding of costs but not rewards by mesolimbic dopamine," is published March 14 in the Proceedings of the National Academy of Science (PNAS).

Researchers from UW departments of psychology, psychiatry and behavioral sciences and pharmacology studied decision-making in adult rats that were provided with continuous access to alcohol during adolescence. Consider a choice between two options - a reward of $50 with 100 percent probability or either $100 or zero dollars with a 50-50 probability. "When you offer these options to people, they tend to take the safe bet," said Jeremy J. Clark, UW acting assistant professor of psychiatry and behavioral sciences. "They'll take the $50," That is just what the control rats did in this study.

However, the alcohol-treated animals consistently choose the riskier option.

One way to produce such risk-taking behavior is to alter the value an individual places on rewards. Alternatively, risk-taking could also result from changing how someone judges risks. Clark said he and his colleagues measured changes in the neurotransmitter dopamine during the presentation of rewards alone and in response to cues predicting risky or certain outcomes to test these possibilities. "Dopamine is central to the way we process and evaluate rewards and is the primary target in the brain for virtually all abused drugs," said Clark. The researchers found that alcohol use during adolescence increased dopamine signaling to risky options but did not affect responses to rewards. "Alcohol is corrupting the ability to make a good decision by altering the perception of risk," said Clark. "It doesn't appear to be about the reward."

"There could be something about the risk itself," said Clark, who described this as akin to a "gambling buzz." On the other hand, it could be that the alcohol-exposed rats are not capable of judging probabilities very well.

Clark said researchers now plan to conduct additional experiments to evaluate these possibilities and determine what the implications are for individuals with substance abuse histories. Study findings may also help inform clinical treatments directed at mindfulness now currently being explored in substance abuse treatment programs.

Funding for the study was supported by a grant from the National Institutes of Health and by the Alcohol and Drug Abuse Institute.